134 research outputs found
Nodeless superconductivity and preserved time-reversal symmetry in the noncentrosymmetric Mo3P superconductor
We report a comprehensive study of the noncentrosymmetric superconductor
MoP. Its bulk superconductivity, with K, was characterized via
electrical resistivity, magnetization, and heat-capacity measurements, while
its microscopic electronic properties were investigated by means of muon-spin
rotation/relaxation (SR) and nuclear magnetic resonance (NMR) techniques.
In the normal state, NMR relaxation data indicate an almost ideal metallic
behavior, confirmed by band-structure calculations, which suggest a relatively
high electron density of states, dominated by the Mo -orbitals. The
low-temperature superfluid density, determined via transverse-field SR and
electronic specific heat, suggest a fully-gapped superconducting state in
MoP, with meV, the same as the BCS gap value in the
weak-coupling case, and a zero-temperature magnetic penetration depth
nm. The absence of spontaneous magnetic fields below the
onset of superconductivity, as determined from zero-field SR measurements,
indicates a preserved time-reversal symmetry in the superconducting state of
MoP and, hence, spin-singlet pairing.Comment: 13 pages, 16 figures, accepted by Phys. Rev.
Growth conditions, structure, and superconductivity of pure and metal-doped FeTe1-xSex single crystals
Superconducting single crystals of pure FeTe1 xSex and FeTe0.65Se0.35 doped
with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd
into Fe ions site have been grown applying Bridgman's method. It has been found
that the sharpness of transition to the superconducting state in FeTe1 xSex is
evidently inversely correlated with crystallographic quality of the crystals.
Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in
FeTe0.65Se0.35 crystals. The remaining examined ions do not incorporate into
the crystal structure. Nevertheless, they form inclusions together with
selenium, tellurium and/or iron, what changes the chemical composition of host
matrix and therefore influences Tc value. Small disorder introduced into
magnetic sublattice, by partial replacement of Fe ions by slight amount of
nonmagnetic ions of Cu (~ 1.5 at%) or by magnetic ions of Ni (~ 2 at%) and Co
(~5 at%) with spin value different than that of Fe ion, completely suppresses
superconductivity in FeTe1 xSex system. This indicates that even if
superconductivity is observed in the system containing magnetic ions it can not
survive when the disorder in magnetic ions sublattice is introduced, most
likely because of magnetic scattering of Cooper pairs.Comment: 18 pages, 12 figures, 3 table
Microstructural magnetic phases in superconducting FeTe0.65Se0.35
In this paper, we address a number of outstanding issues concerning the
nature and the role of magnetic inhomogenities in the iron chalcogenide system
FeTe1-xSex and their correlation with superconductivity in this system. We
report morphology of superconducting single crystals of FeTe0.65Se0.35 studied
with transmission electron microscopy, high angle annular dark field scanning
transmission electron microscopy and their magnetic and superconducting
properties characterized with magnetization, specific heat and magnetic
resonance spectroscopy. Our data demonstrate a presence of nanometre scale
hexagonal regions coexisting with tetragonal host lattice, a chemical disorder
demonstrating non homogeneous distribution of host atoms in the crystal
lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From
magnetic data and ferromagnetic resonance temperature dependence, we attribute
magnetic phases in Fe-Te-Se to Fe3O4 inclusions and to hexagonal symmetry
nanometre scale regions with structure of Fe7Se8 type. Our results suggest that
nonhomogeneous distribution of host atoms might be an intrinsic feature of
superconducting Fe-Te-Se chalcogenides and we find a surprising correlation
indicating that faster grown crystal of inferior crystallographic properties is
a better superconductor.Comment: 16 pages, 8 figures, 2 table
Microscopic study of the impurity effect in the kagome superconductor La(RuFe)Si
We report on the effect of magnetic impurities on the microscopic
superconducting (SC) properties of the kagome-lattice superconductor
La(RuFe)Si using muon spin relaxation/rotation
(SR). A strong suppression of the superconducting critical temperature
, the SC volume fraction, and the superfluid density was observed.
We furthermore find a correlation between the superfluid density and which is considered a hallmark feature of unconventional superconductivity.
Most remarkably, measurements of the temperature-dependent magnetic penetration
depth reveal a change in the low-temperature behavior from
exponential saturation to a linear increase, which indicates that Fe doping
introduces nodes in the superconducting gap structure at concentrations as low
as ~0.015. Our results point to a rare example of unconventional
superconductivity in the correlated kagome lattice and accessible tunability of
the superconducting gap structure, offering new insights into the microscopic
mechanisms involved in superconducting order.Comment: 7 page article with 4 figure
Morphological Identification and Single-Cell Genomics of Marine Diplonemids
Recent global surveys of marine biodiversity have revealed that a group of organisms known as “marine diplonemids” constitutes one of the most abundant and diverse planktonic lineages 1. Though discovered over a decade ago 2, 3, their potential importance was unrecognized, and our knowledge remains restricted to a single gene amplified from environmental DNA, the 18S rRNA gene (small subunit SSU). Here, we use single-cell genomics (SCG) and microscopy to characterize ten marine diplonemids, isolated from a range of depths in the eastern North Pacific Ocean. Phylogenetic analysis confirms that the isolates reflect the entire range of marine diplonemid diversity, and comparisons to environmental SSU surveys show that sequences from the isolates range from rare to superabundant, including the single most common marine diplonemid known. SCG generated a total of ∼915 Mbp of assembled sequence across all ten cells and ∼4,000 protein-coding genes with homologs in the Kyoto Encyclopedia of Genes and Genomes (KEGG) orthology database, distributed across categories expected for heterotrophic protists. Models of highly conserved genes indicate a high density of non-canonical introns, lacking conventional GT-AG splice sites. Mapping metagenomic datasets 4 to SCG assemblies reveals virtually no overlap, suggesting that nuclear genomic diversity is too great for representative SCG data to provide meaningful phylogenetic context to metagenomic datasets. This work provides an entry point to the future identification, isolation, and cultivation of these elusive yet ecologically important cells. The high density of nonconventional introns, however, also portends difficulty in generating accurate gene models and highlights the need for the establishment of stable cultures and transcriptomic analyses. © 2016 Elsevier Lt
Hidden magnetism uncovered in charge ordered bilayer kagome material ScV_6Sn_6
Charge ordered kagome lattices have been demonstrated to be intriguing
platforms for studying the intertwining of topology, correlation, and
magnetism. The recently discovered charge ordered kagome material ScV_6Sn_6
does not feature a magnetic groundstate or excitations, thus it is often
regarded as a conventional paramagnet. Here, using advanced muon-spin rotation
spectroscopy, we uncover an unexpected hidden magnetism of the charge order. We
observe a striking enhancement of the internal field width sensed by the muon
ensemble, which takes place within the charge ordered state. More remarkably,
the muon spin relaxation rate below the charge ordering temperature is
substantially enhanced by applying an external magnetic field. Taken together
with the hidden magnetism found in AV_3Sb_5 (A = K, Rb, Cs) and FeGe kagome
systems, our results suggest ubiqitous time-reversal symmetry-breaking in
charge ordered kagome lattices.Comment: 9 pages, 4 figure
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